v8.0 module release (#22975)

https://mattermost.atlassian.net/browse/MM-52079

```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```


Co-authored-by: Doug Lauder <wiggin77@warpmail.net>

server/model/group_syncable_test.go

@@ -0,0 +1,20 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGroupSyncableMarshal(t *testing.T) {
+	require.NotPanics(t, func() {
+		var syncable GroupSyncable
+		_, err := json.Marshal(&syncable)
+		require.Error(t, err)
+		t.Log(err.Error())
+	}, "marshaling groupsyncable should not panic")
+}